A model for the structure of metallic glasses based on chemical twinning

Abstract

A model for transition-metal-metalloid glasses has been constructed and refined by energy minimization with the use of a Lennard-Jones 6-12 potential. The model is based on the concept that domains of positionally correlated atoms exist in these glasses on a scale of 1-2 nm. Within each domain, positional order is governed by rules appropriate to a single type of structural operation (simple chemical twinning in this case) acting in a prescribed direction. (The structure of compositionally equivalent crystalline phases may be represented by similar rules acting over essentially infinite domains.) Positions of atoms in the interface between domains are defined by two (or more) operations appropriate to each of the bounding domains so that the structure has a high degree of homogeneity. Computed properties are compared with experimental structural data for a number of typical amorphous transition-metal-metalloid alloys. Agreement between experimental and calculated partial pair-correlation functions and structure factors is good, supporting the notion of extensive local and medium-range positional order in these alloys. Moreover, the discrepancies that exist between model data and experimental results suggest that the model is less ordered than an actual glass. This model provides some insight into the nature of local geometrical distortions of structural units, coupling between positional and compositional fluctuations and the relative stability of glassy and microcrystalline alloys.